There are biological and chemical effects known to occur from exposure intensities comparable to those used in clinical ultrasound. However, the relationship between the laboratory-derived results and the issue of clinical health and safety can only be made if the physical mechanism(s) of action causing the laboratory-derived effects is (are) understood. The proposed research will attempt to verify and provide a mechanistic understaning of several reported biological effects of diagnostic ultrasound, namely: 1) the presence of unscheduled DNA synthesis in ultrasonically exposed HeLa cells; (2) the possibility of an increased frequency of sister chromatid exchanges in ultrasonically exposed human lymphocytes; and (3) the ability of ultrasound exposure to induce oncogenic transformation in the BALB/c cell line. Additionally, the research will further test a proposed model which has been postulated to be responsible for observed biological and chemical effects of pulsed ultrasound when exposure occurs in a rotating polystyrene test tube. The present data indicates that at a constant pulse repetition rate but variable intensity and pulse duration, the presence of acoustic cavitation is enhanced with shorter pulse durations at higher intensities. The model, which predicts this trend should continue, will be tested by protocols involving various surfactants (to reduce bubble surface tension), pulse lengths, pulse repetition rates and intensity combinations in the presence of an assay for acoustic cavitation.